This invention pertains to a method of forming close tolerance high quality holes in fiber reinforced composite materials. The prior methods for producing high quality holes in laminated composite materials required a series of operations. First, the composite structure was formed by, for instance, laying up a series of impregnated fiber layers and then completely curing the composite under heat, pressure, and the required vacuum conditions. Second, a pilot hole was drilled in the composite material, usually with a carbide or diamond drill, followed by an undersized hole. Finally, to bring the hole into tolerance it was reamed to the proper dimensions and then countersunk as necessary. Several dificulties may be encountered during the drilling procedure, such as material breakout or delamination on the front and back face of the composite laminate due to drilling pressure or upon drill removal, and overheating of the composite. When a hole is drilled in a composite, hazardous dust may be formed which requires special handling, such as hoods, enclosures and othe means to protect the working environment. Hole surface abrasion may be caused by abrasive shavings from the drilling procedure and especially so when drilling through graphite and metal simultaneously. Dull drill bits or lack of a proper coolant causes overheating of the composite materiall resulting in residual stresses, charring and aperture wall glazing. Even when proper coolant is utilized there is the possiblity of aperture wall contamination by the coolant and coolant migration into the laminate. Any flexibility in the holding fixture for the composite part, or asymmetry in drilling and grinding or excessive accumulation of swarf can produce out-of-tolerance, out-of-round holes, or unacceptable hole surface finishes.
An array of precision tools may be required to complete the close tolerance holes in high strength composites such as graphite epoxies. Among the tools utilized in forming the holes in the graphite epoxy laminates are carbide pr carbide-tipped drill bits and carbide or diamond reamers, both of which are expensive and have a limited useful life. Upon completion of the hole in the composite, the hole size and quality may have to be examined by one or more non-destructive evaluation (NDE) techniques including ultrasonic C-scan, boroscope inspection, as well as dimensiional checks and visual inspection. All of these various manufacturing and inspection techniques for hole fabrication are both expensive and time consuming.